Conventionally, a laminate sheet prepared by laminating plural sheet materials has been used for various uses. For such a laminate sheet, the material characteristics of the respective layers can be reflected in the characteristics of the laminate sheet by laminating different sheet materials. The patent reference 1 discloses that a sheet material having an excellent heat resistance and a sheet material having an excellent insulating performance are laminated together for use as an interphase insulation sheet for a motor.
In addition, for such a laminate sheet, a resin composition is commonly used for laminating plural sheet materials. Therefore, for the resin composition, the characteristics adapted to the intended use is also required.
Furthermore, since the thickness accuracy of the resin composition also affects the characteristics of the laminate sheet, for example, the extruding of the resin composition with a uniform thickness such as by a T-die has been carried out in a laminating process.
Meanwhile, polyamide resins are known to easily form hydrogen bond at amide group in the main molecular chain, to have strong intermolecular force owing to the hydrogen bond, and to easily show crystallinity. Because of the property to easily show crystallinity, the polyamide resins are superior to other resins in terms of heat resistance, resistance to hydrolysis, and other characteristics, and have dynamic strength.
Especially, an aromatic polyamide having an aromatic ring in the main molecular chain has a higher heat resistance and can also lower water absorbency because it has a rigid aromatic ring in the main molecular chain, as compared with an aliphatic polyamide in which an aliphatic compound is used. Accordingly, the aromatic polyamide has been widely used in the fields in which a high heat resistance and a lower water absorbency are required in order to improve these characteristics.
However, when this aromatic polyamide is to be used as a resin composition to laminate the sheet material, it tends to have fewer entanglements of molecules in molten state than those of aliphatic resins because it has a rigid aromatic ring in the main molecular chain. Therefore, for a resin composition that uses an aromatic polyamide in a temperature region higher than the melting point the flowability becomes excessively high, a moderate flowability with 30 or smaller MFR that is suitable for the extruding by such as T-die can not be achieved, and accordingly it is difficult to extrude onto a sheet material.
To this point, there is a proposal that the extruding is performed by lowering the extruding temperature to near the melting point. The polyamide resins, however; show abrupt phase change near the melting point compared with other resins because they easily show crystallinity. Furthermore, for an aromatic polyamide resin, the flowability over the melting point is higher comparing aliphatic polyamide resins, and the flowability at near the melting point is also precipitous, from the reason as mentioned above. Therefore, from the fact that when the extruding is performed by lowering the temperature, the flowability greatly changes even by the little temperature change of an extruder and variations in extrusion rate occurs, it becomes difficult to extrude with a uniform thickness. Accordingly, in order to maintain the thickness accuracy of the laminate sheet, precise temperature control is required. However it is practically difficult to precisely maintain the extruding temperature.
That is, conventionally, for a laminate sheet prepared by laminating plural sheet materials with a resin composition, an aromatic polyamide has been used as the resin composition to laminate the sheet materials, and it has a problem that it is difficult to obtain easily producible products while improving the heat resistance and the water absorbency.
Patent document 1                Japanese patent application laid-open no. no. hei-9-23601        